System of radio communication



Oct. 20, 1931.

H. C. FORBES SYSTEM OF RADIO COMMUNICATION Filed Sept. 16, 1926 2 Sheets-Sheet l :Mzy 0.2 67 56 Oct. 20, 1931. .H. c. FORBES 1,828,529

SYSTEM OF RADIO COMMUNICATION 7 Filed Sept. 16', 1926 2 Sheets-Sheet 2 Patented Oct. 20, 1931 UNITED STATES PATENT oF-F1cr. Q

HENRY c} ronnns, or CHICAGO, ILLINOIS, zissreivon r0 ZENITH nAnIo 'conrom- TION, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS SYSTEM OF RADIO COMMUNICATION Application filed September 16, 1926. S eriaINo. 135,824.

My invention relates to, systems of radio communication and is ofparticular use in those systems wherein the sending and receiving stations are not far apart. L

The system of my invention is especially useful when employed in establishing communication between stations upon locomotives and the cars of a train. The invention is of much service in establishing communication between attendants upon the locomotives and cabooses of freight trains.

ljvhile the invention thus finds especial utility, it is not to be limited to any particular use;

" It is the object ofmy invention to include signaling apparatus in the system whereby an operator or attendant at either station may signal an operator or attendant at the other station. Generally speaking, theradio system of communication of my invention employs an antenna, a circuit having apparatus therein for generating and impressing upon said antennaa wave form carrier current, a

telephonic circuit including a telephonic transmitter, a signaling circult including means for producing wave form signaling current,- and means forassociatlng said carrier current circuit with either said telephonic or signaling circu t. In the preferred embodiment of the invention, means for generating wave form carriercurrent resides in an oscillating thermionic valve. I also desirably employ another thermionic valve individual to the wave form carrier current I circuit and common to the telephonic trans-1 mitting circuit and the signaling circuit and serving as a modulator under thecontrol of the telephonic currents and as a generator of signaling current. Transformers couple the modulating thermionic valve with the telephonic and signaling circuits, switching means being employed for interchangeably associating this valve with said telephonic and signaling circuits.

The signaling apparatus erably secured by a modulation of the carrier current'wave by a signaling current wave of which Figs. 1,

illustrations of V desirably furnishes audible signals, a result whichis pref the receiving station and preferably in a loud ble through the rumblingnoises made by the moving train and the higher pitched noises such as those caused by steam whistles.

I will explain my invention more fully by reference to the. accompanying drawings in 2, 3 and 4 are diagrammatic various embodiments of the mvention. I

The varioussystems illustrated are, in most respects, very similar, like parts'in the different systems being given similar characters of reference. ,The following descri tionrefers toeach system except where di erences between the systems" are noted. a The antenna 1 is grounded througha winding 2. A winding 3, in conjunction with the winding 2 to which itis inductively related couples the antenna with a circuit in which a wave form carrier current is generated and upon which slgnahng and telephomc currents are adapted to be impressed. This connected with the plate 6 through the condenser 10. The filament? isfsuppliedwith current from a battery 11. A source ofdirect current 12 is connected between the fila- .ment 7 and the plate 6 byway of the air core choke coil 13, the .iron core impedance coil or winding 14 and a secondary winding 15, in the formfof the invention illustrated in Fig. 1, which pertains to the signaling apparatus of my invention as will'm'ore fully appear, hereinafter. The conductor 16 by which one pole of the generator 12'and one pole of the battery 11' are connected with the filament 7 is desirably also connected o with the antenna and has an adjustable connection 17 with, the winding3. The antenna. 1 is thus coupled with acircuit in whichiwave form carrier current is generate sending station causing an audible'signal at aid wave form carrier current In addition to the oscillator circuit, which has been described, I employ a modulator circuit which includes a thermionic valve 18 which employs a grid 19, a plate 20, and a filament or cathode 21. The plates 6 and are connected together, the impedance winding 14 being connected between the plate 20 and the choke coil 13. The filament 21 is supplied with current from the aforesaid battery 11. The grid 19 is connected with a switch arm 22. This switch arm is coupled by a lever 23 with another switch arm 24, the two switch arms being movable in unison by moving said lever 23. When the lever is thrown into the position illustrated, the valve 18 is included in the signaling system of my invention by way of the arm 22, the switch arm 24,, which pertains to the telephonic transmission circuit, as will more fully later appear, being then open. This valve 18 then operates, in accordance with the preferred ,way of practicing my invention, as a generator of audio frequency wave mg current whichis conveyed by way of this 25' form signalvalve to the wave form carrier current c1rcult, the antenna belng consequently 1mpressed' with a carrier wave which 1s effective to operate the loud speaker or other responstation being signalled.

sive device at the In the system shown in Fig. 1 this signaling circuit includes a battery 25 and a primary 26 complemental to the secondary 15 in the wave form carrier current circuit, the transformer 1526 being the means relied upon in the system of Fig. 1 for impressing the circuit with the wave form signaling currents of audio frequency initiated in the inducing signaling circuit. In the system shown in Fig. 2, the

, primary winding 26 is in inductive relation to the impedance winding 14, the latter winding having thus added to it the function of winding 15 of the system of Fig. 1.

After'the signaling has been effected, the

lever'23 is reversed to open the signaling cir- V c'uit and to cause the switch arm 24 to close a local telephonic circuit which includes a telephonic transmitter 27, a battery 28 and I the primary 29 of an inductive coupler. The

switch arm 22, at the same time, includes a secondary 3O complemental to the primary 29 between the grid 19 and the battery 25 in lieu of theprimary winding 26 of the signaling circuit. The valve 18, which functioned as a generator of audio frequency signaling current when the signaling circuit was closed now functions as a modulator under the control of the telephonic currents. When the telephonic transmitter is not operating, the potential difference between the termi- U nals of thebridge that includes the generator 112 and the winding 14 is constant, wherefor the amplitude of the high frequency antenna current, as well as the plate current for the modulator thermionic valve 18 is constant.

When the telephonic transmitter is spoken into, electromotive forces are induced in the secondary coil 30, which change the potential of the grid of the thermionic modulator valve 18 in accordance with the vibrations of the transmitter. This causes the plate current of the modulator to change at speech or audio frequency. The generator 12 will, consequently, be called upon to supply a current varying at audio frequency and which must flow through the iron core impedance winding 14. Since the impedance of this winding is very high at audio frequency, it follows that it will causea large audio frequency drop of potential over itself,,wherefor the potential difference between the terminals of the bridge that include the elements 12 and 14 will be varied at audio frequency and in accordance with the vibrations of the telephonic transmitter. The amplitude of the antenna carrier wave will, consequently, be varied, since this amplitude varies with the plate voltage. The vibrations of the telephonic transmitter are finally reproduced in the antenna as variations in the amplitude of the antenna carrier wave, that is, the antenna carrier wave is thus modulated.

In the system shown in Fig. 3, an 8-shaped magnetizable core 31 is employed upon whose outer sides the two halves of the winding 29 are disposed. The windings 26 and are also disposed upon the outer sides of this core, the Winding 26 being so connected that it not only serves-as a signal current inducing coil when the switch is in signaling position but also serves, in conjunction with coil 30, as a secondary to the telephonic primary winding 29. The winding 14 is upon the middle member 32 of the core 31. The windings 26, 29, and 30 are of such direction that they send flux around the core without sending any flux through the middle member 32 of the core. Consequently, when the system of Fig. 3 is adjusted to a talking condition, speech modulating currents, passing through the coil 29in series,ind'uce currents in the windings 26 and 30 thereby performing the functions of the induction coils 29, 30, in the systems of Figs. 1 and 2. Since there is no flux through the center portion 32 of the core, there is nothing to disturb the functioning of the coil 14 in its normal capacity of a choke coil. Conversely, currents in this winding 14 have no effect upon the two coils of the winding 29 in series and upon the windings 26'and 30 in series. WVhen the system is adjusted to a signaling condition, the windings 29 and 30 are open circuited, the winding 26 being then in inducing relation tothe winding 14 as in the system of Fig. 2.

In the system illustrated in Fig. 4, an amplifying thermionic valve 33 isinterposed between the modulator valve 18 and the telephonic transmitter and signaling circuits. The plate 34 of this valve is connected with the grid 19 of the valve 18 through a condenser 35 and a bridge 36 is extended be tween the conductor 16 to a point between the grid 19 and the condenser 35, this bridge containing a resistance 37 and a battery 38. The secondary signal transformer coil 39 is connected between the plate 34 of the valve 33 and the bridge which contains the generator 12 and impedance winding 14. The signalling current primary winding 40 is connected with the grid 41 of the thermionic valve 33 when the circuit is adjusted to signaling condition. The valve 33 thus serves as a generator of audio frequency wave-form signaling current when the equipment is adjusted to signaling position and as an. amplifier of, and primary modulator under the control of, telephonic currents when the system is adjusted to talking position.

Changes may be made without departing from the invention.

Having thus described my invention, I claim:

1. In a radio system of communication, the combination with an antenna and a circuit having means therein for generating and impressing upon said antenna a wave form car rier current; of atelephonic. circuit includ ing a telephonic transmitter; a signaling circuit including a thermionic valve individual to said wave form carrier current circuit and serving as a generator of audio frequency signaling current; and means for disconnecting said valve from said signaling circuitand associating it with said telephonic circult to serve as a modulator under the control of the telephonic currents. i

2. In a radio system of communication, the combination with an antenna and a circuit having means therein for generating and impressing upon said antenna a wave form carrier current of a transformer secondary winding in the aforesaid circuit; a telephonic circuit including a telephonic transmitter; a signaling circuit including a primary to the aforesaid transformer secondary winding and a thermionic valve serving as a generator of audio frequency signaling current; and means for disconnecting said valve from said signaling circuit and associating it with said telephonic circuit to serve as a modulator under the control of the telephonic currents.

3. In a radio system of communication, the combination with an antenna and a circuit having apparatus therein for generating and impressing upon said antenna a wave form carrier current; of a telephonic circuit including a telephonic transmitter; a signaling circuit including means for producing audio frequency wave form s gnahng current; and means for disconnecting said audio frequency wave producing means from said signaling circuit and associating it with said telephonic circuit to serve as a modulator under the control of the telephone curcuit to serve said signaling circuit.

rents, whereby" said carrier current circuit may be alternately associated with said telephonic circuit and with said signaling circuit. 4. In a radio system of communication, the combination with an antenna and a circuit having apparatus therein for generating and impressing upon said antenna a wave form carrier current; of a telephonic circuit including a telephonic transmitter; a signaling circuit inclu'ding a thermionic Valve for producing audio frequency wave form signaling current; and meansfor disconnecting said thermionic valvefrom said signaling circuit and associating'it with said telephonic ciras a modulator under the control of the telephonic currents, whereby said carrier current circuit may beassociated at Will with either said telephonic circuit or with ation, the a c1rcu1t having 5. In a radio system of communic combination with an antenna, means for generating and impressing upon said antenna a wave form carrier current and lncluslve of an oscillating thermionic valve, a source of current supplying said valve, and an lmpedance' winding through which cur rent is supplied from said source; of a second thermionic valve coupled with the aforesaid circuit and included in a signaling circuit containing a transformer primary winding; a local telephonic circuit containing a transformer primary windingand a telephonic I transmitter; a transformer secondary windmg for the latter primary winding; a ma netizable 8 -sh aped core having said imped ance w1n d1ng upon its middle member and the remalning windings upon other portions thereof; and means for disconnecting said second thermionic valvefrom said signaling 1 05 c rcuit and associating it with said telephonic circuit, this valve when included in said signahng clrcu t serving as a generator of audio frequency signaling current, and when associated with said telephonic circuit servin as a modulator under the control of the tele phomc currents.

' 6. In a radio system of communication, the combination with an antenna and a circuit having means therein for generating and impresslng upon said antenna a wave form car'- rler current; of a telephonic circuit includin a telephonic transmitter; a signaling circuit including a thermionic valve individual to said wave form carrier current circuit and serving as a generator of audio frequency signaling current; and means for disconnecting said valve from said signaling circuit andcoupling it with said telephonic circuit to serve as anamplifier of the telephonic currents and to impress such amplified telephonic currents as modulations upon said carriercurrent circuit.

7. In a radio s ystem of communication, the

combination, with an antenna and a circuit having means therein for generating and impressing upon said antenna a wave form carrier current, of a transformer secondary'winding in said circuit, a telephonic circuit including a telephonic transmitter and a transformer primary winding, a plurality of transformer windings, the first of which is a primary to said secondary winding and the second of which is a secondary to said primary winding, a thermionic valve individual to said wave form carrier current circuit, and means operable at will to selectively connect the input of said valve with either of said plurality of transformer windings.

8. In a radio system of communication, the combination, with an antenna and a circuit having means therein for generating and impressing upon said antenna a Wave form carrier current, of a transformer secondary winding in said circuit, a telephonic circuit including a telephonic transmitter and a transformer primary winding, a plurality of transformer windings, the first of which is a primary to said secondary winding and the second of which is a secondary to said primary winding, a thermionic valve individual to said wave form carrier current circuit, and means operable at will to selectively connect the input of said valve with the first of said plurality of transformer windings and open said telephonic circuit or to connect the input of said valve with the second of said plurality of transformer windings and close said telephonic circuit.

In witness whereof, I hereunto subscribe my name.

HENRY C. FORBES 

